Air source heat pump/immersion heater query

[Welderpaul]

I'll start a new thread as the last one got buried. Slightly different topic anyhow.

Ongoing saga of air source heat pump being poor in cold weather.
Extract below from cylinder diagram. Bottom immersion - in green - has an electrical feed. The bottom part of the tank is either a buffer or a volumiser depending how it is configured (Don't know which).
The top part is the primary circuit. This immersion - in red - is not wired and never has been. Not sure why this has not been wired.
I can't see any reason why i can't put a supply to this to help heat the DHW and rads when the air source heat pump is struggling?

Any thoughts kind chaps?

 

[Neilj]

If your heat pump is struggling to heat the DHW then the immersion will help in two ways; it'll heat the DHW plus it gives the heat pump less work to do and you'll get a bit more energy from the heat pump into your space heating.
The only drawback is the cost, full price leccy to power the thing. I'm curious how efficient a heat pump is at heating DHW to 55-60 Deg when the outside temperature is like it is now, can't be very efficient so maybe not much difference between the immersion and heat pump?

 

[Welderpaul]

Yep, I get the loss of efficiency etc plus it will deal with the immediate issue
The Immersion is 3KW

 

[sparkysy]

How is the bottom immersion heater controlled is it through the heating system or just on a spur/20a switch?
If it is through the heating system then it may be timed or thermostat controlled or both (as well as inbuilt stat in heater)
The top element may well improve heat temperature and reduce demand on the ASHP but it will cut out earlier on the inbuilt stat than the bottom one due to heat rising. Can't hurt to try it!
Sy

 

[Welderpaul]

How is the bottom immersion heater controlled is it through the heating system or just on a spur/20a switch?
If it is through the heating system then it may be timed or thermostat controlled or both (as well as inbuilt stat in heater)
The top element may well improve heat temperature and reduce demand on the ASHP but it will cut out earlier on the inbuilt stat than the bottom one due to heat rising. Can't hurt to try it!
Sy

@sparkysy It comes direct from a DP switch. There is a single 2.5 T&E to the DP switch. I'll need to pull some trunking capping off to trace the cable. I wonder why it was never wired when it was installed.

I was going to run a temporary feed to the upper immersion just to see what difference it makes?

If it does prove to be of a benefit to have it connected, two 3KW immersions from one 2.5 T&E will overload the cable?

 

[brightspark]

@sparkysy It comes direct from a DP switch. There is a single 2.5 T&E to the DP switch. I'll need to pull some trunking capping off to trace the cable.

I was going to run a temporary feed to the upper immersion just to see what difference it makes?

If it does prove to be of a benefit to have it connected, two 3KW immersions from one 2.5 T&E will overload the cable?

will need 2 supplies 3kw on each using 2.5mm and fed of 16 amp mcbs

 

[Welderpaul]

will need 2 supplies 3kw on each using 2.5mm and fed of 16 amp mcbs

OK, its a fair run from the DB but a fairly easy route. I have a spare way in the board. Probably about 20M run.
Can I run it from a 13A socket just to test it short term?

 

[brightspark]

OK, its a fair run from the DB but a fairly easy route. I have a spare way in the board. Probably about 20M run.
Can I run it from a 13A socket just to test it short term?

yes will be ok .plug may get slightly warm after a while but nothing to worry about

 

[Bornfree]

Heat pumps normally use immersions to heat the system up to 60° to kill off any legionella that can build up in 30-40° water.

 

[Tigman]

It reads to me that the buffer emersion comes on to help the heat pump , that's the green one ! The other emersion is for when the heat pump is not in use , it Wont do any harm to use it just can extra cost !

 

[Neilj]

Bottom immersion is more than likely connected to the heat pump, so it can boost the buffer tank (heating loop) if required. Nothing to do with your DHW that one.

 

[voipio]

Is the hot water cylinder compartmentalised? If it's not, I can't see how the bottom immersion heater cannot heat the contents of the hot water cylinder, unless it's thermostat is set to a low temperature.

 

[Welderpaul]

Is the hot water cylinder compartmentalised? If it's not, I can't see how the bottom immersion heater cannot heat the contents of the hot water cylinder, unless it's thermostat is set to a low temperature.

It is compartmentalised, yes.

 

[addjunkie]

It reads to me that the buffer emersion comes on to help the heat pump , that's the green one ! The other emersion is for when the heat pump is not in use , it Wont do any harm to use it just can extra cost !

Thats the way it reads to me too, and I expect that from a air source system as they are known inefficient at low tempratures, hence why I asked in the other thread if there was a heat store tank to increase volume. If that tank is sectioned it is ineffect the same thing. Id ecpect that to have some control via the system rather than just a dp switch.

Do you have a clamp electrical meter to check if its in use? Was the plumbing andwiring done by the same firm, and didwhich ever sparky who connected it up understand Air source and why it might have two emersion’s? Also does yourtank have both thermostats fitted of just 1, if so which i e and whats it set at

Id have a solar economiser on both of those, there are others, if you have panels.

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[frank horton]

sorry Paul I feel ur pain....

a good friend had a new comp system installed by profs.....
with under floor heating..
he lived in the warm SW France, with the odd frost and short winters......
total waste of money, he used a wood stove to heat the house...!!!!
in the end, until the house was sold he decommisioned it and just used wood.......read cheaper.....
I told him to get a wood stove with a back boiler in the first place.....

AND this is the efficient future........dont make me laugh.....
Politions know f'all about nuffin except filling their pockets.....

what did Mr T say......"u suckers".....hahaha...

 

[brewdexta]

My brother has 4 holiday lets all working on GSHP or ASHP, no issues. They are old converted farm buildings, some are 3 beds with large kitchens/living rooms and several bathrooms so not tiny. So they can work.

The only issue he has had was the slinkies (coils of pipe laid in a trench in the ground for the GSHP) perforated after about 5 years, probably because of incorrect installation, so he now uses a bore hole. He was an early adopter of the tech so probably improved by now,

 

[addjunkie]

My brother has 4 holiday lets all working on GSHP or ASHP, no issues. They are old converted farm buildings, some are 3 beds with large kitchens/living rooms and several bathrooms so not tiny. So they can work.

The only issue he has had was the slinkies (coils of pipe laid in a trench in the ground for the GSHP) perforated after about 5 years, probably because of incorrect installation, so he now uses a bore hole. He was an early adopter of the tech so probably improved by now,

Logically a bore hole though expensive to drill will be far more efficient. Ground gets a fair bit warmer as you drill down.

 

[brewdexta]

Logically a bore hole though expensive to drill will be far more efficient. Ground gets a fair bit warmer as you drill down.

Also easier to get the pipe immersed in water to extract the heat. Slinkies aren't always as good in that respect. I do know somebody who put pipe in the drainage ditches around his property for the heat pump, but he had a big old pile with oodles of land.

 

[addjunkie]

Also easier to get the pipe immersed in water to extract the heat. Slinkies aren't always as good in that respect. I do know somebody who put pipe in the drainage ditches around his property for the heat pump, but he had a big old pile with oodles of land.

I did look at doing it. My front field has a very wet strip with a spring under it, too wet to use tractor over it, except in a heat wave. When I applied for planning National Park were well please I wanted new modern tech But……I had to have an archieologist on site for the duration, and if anything was found, it would stop the job, also newt etc surveys. I was told a bore hole at the back ok just drill away, but it was 13k, 10 years ago. Looked at hiring the rig my self with-a neighbour. To drill mine and 3 for him 2 wells and a bore hole for a heat pump, Hes a directional driller in the oil buisness, so knows his onions, I worked in drilling 30years sohave 1/2 a clue. But we were only going to save about 8 grand and carry all the risks ourselves.

An oil boiler was 2 k.

 

[Welderpaul]

How is the bottom immersion heater controlled is it through the heating system or just on a spur/20a switch?
If it is through the heating system then it may be timed or thermostat controlled or both (as well as inbuilt stat in heater)
The top element may well improve heat temperature and reduce demand on the ASHP but it will cut out earlier on the inbuilt stat than the bottom one due to heat rising. Can't hurt to try it!
Sy

@sparkysy I think you are correct. This is the feed to the bottom immersion. The bit on the left is a contactor, and a time clock on the right.
I guess timed to come on to kill off legionella. The bottom right green button is an override switch but it might be controlled by something else too?
Could do with being able to switch this on.